1. Technical Field
The present invention relates to data communications systems and, in particular, to the establishment of multiple related communication data links between two computer systems and the utilization of one data link for error correction. Still more particularly, the present invention relates to a method and system in a data communications system for the transmission of data packets utilizing a first data link and the transmission of selective rejection packets and their associated retransmissions of data packets utilizing a second, related data link.
2. Description of the Related Art
Computer systems utilize modems to communicate with each other utilizing analog telecommunication lines such as a telephone network. The modem converts the digital data from the computer to an analog signal that can be transmitted on a telecommunication line, and converts the analog signal received to data for the computer. Standard protocols are defined, such as the ITU V series, which describe modem operation and design in order to permit different, conforming computer systems to communicate.
One such protocol is an error detection and recovery via retransmission protocol, such as the ITU V.42 protocol. Such a protocol recovers from errors by retransmitting incorrectly received data packets. Error correction protocols are defined to overcome data communication errors typically due to noise on the telecommunication line. The protocol defines procedures to be taken when a transmitted packet of data is received in error.
For example, when a receiving system receives a packet in error, a standard reject procedure (REJ) requires the retransmission of all data received after the bad packet was received. Alternatively, a selective reject procedure (SREJ) requires retransmission of only the packets which were actually received in error, thus minimizing the total amount of data which must be retransmitted after an error has occurred.
Using a selective reject instead of a standard reject procedure may speed up transmission. However, problems can occur when the packet including the selective reject information is itself in error. For example, the selective reject packet may be lost during transmission. In this case, the data link must wait for a time-out recovery. This wait may have a larger negative impact on throughput than if a standard reject procedure had been used, since all data sent while waiting for the time-out will be discarded during the process of recovering from that time-out.
Therefore a need exists for a method and system in a data communications system such that data packets may continue to be transmitted although errors may occur during the transmission of selective rejection packets.